1. Field of the Invention
The present invention relates to an image forming system that forms an image according to a printing medium, and a control method thereof.
2. Description of the Related Art
Conventionally, a commercial printing firm receives a request to create a printed product (e.g., magazine, news paper, catalogue, advertisement, or gravure) from a customer or a client. The commercial printing firm then creates and delivers the printed product desired by the client and receives payment from the client. Currently, such commercial printing firms mainly use large-scale printing apparatuses such as an offset type printing machine, so that various processes are established in the commercial printing industry. The processes include uploading, design, layout, comprehensive layout (i.e., presentation by printer output), proofing (e.g., layout proofing and color proofing), proof printing, printing plate creation, printing, post processing, and shipping. The printing plate creation is an essential process among the above-described processes, and it is not easy to correct the printing plate once the printing plate is created. Further, it is disadvantageous in terms of cost to correct the printing plate, so that it is necessary to carefully perform proofing, i.e., to check the layout and confirm the colors. Since the above-described large-scale apparatuses and operation processes are necessary for the commercial printing firm to create the printed product desired by the client, a certain amount of time becomes required to create the desired product.
On the other hand, improvements in speed and image quality of electrophotographic and inkjet type printing apparatuses have lead to a growth in a print on demand (POD) market. In contrast to the above-described commercial printing firms, digital image forming apparatuses such as a digital copying machine and a digital multifunction peripheral (MFP) are used in the POD market. The POD market is directed to handling jobs of a comparatively small lot within a short delivery time, without using the large-scale printing apparatus or system. As a result, digital printing employing digital data has become widespread, instead of the printing method employed by the above-described commercial printing firms. There is thus a demand for printers and digital copying machines to have functions equivalent to functions that are often used in commercial printing firms.
Japanese Patent Application Laid-Open No. 2004-058508 discusses an apparatus and a method for printing an index on a tab sheet, i.e., a sheet having an index portion, and inserting the tab sheet in a desired position of the printed product.
However, a precondition for the technique discussed in Japanese Patent Application Laid-Open No. 2004-058508 is to prepare a predetermined tab sheet bundle and then to print on such a bundle. The predetermined tab sheet bundle is a bundle of tab sheets in which the index portions of the tab sheets are aligned in order from the bottom portion of the sheet to the top portion of the sheet (hereinafter referred to as an ascending order type tab sheet bundle). Further, the index portions are aligned in order from the top portion to the top bottom of the sheets (hereinafter referred to as a descending order type tab sheet bundle). It is thus not suitable to perform continuous printing of the printed output, and it becomes necessary to reset printing sheets for each print job. Further, if both of the ascending order type sheet bundle and the descending order type sheet bundle are stored in the digital image forming apparatus for performing continuous printing, the wrong tab sheet bundle may be fed when an automatic sheet selection is set.
Furthermore, if the tab sheet bundle runs out during printing, sheet feeding stages inside the image forming apparatus are searched using “tab sheet” as a keyword, so that the image forming apparatus may continuously feed the wrong tab sheet bundle. It is thus desirable to solve such problems and improve user-friendliness.